As one of criteria in order to execute a stable blast furnace operation, brightness information of a raceway portion in a blast furnace that is observed through a tuyere of the blast furnace is employed. The brightness information includes pieces of information important in an operation of the blast furnace, such as a level of furnace heat, a combustion degree of pulverized coal, and drop information of non-melted iron ore. Observation of the brightness information through the tuyere is performed by sensory inspection in which an operator looks into an observation window approximately several times per day. In recent years, a camera is installed in the vicinity of the tuyere and images (tuyere images) shot by the camera are displayed on a monitor in a monitoring room so as to be centrally monitored in increased cases (for example, see Patent Document 1).
Note that a plurality of tuyeres are provided in the circumferential direction of the blast furnace. In any of the cases where the operator directly looks into the observation window and where the operator centrally monitors in the monitoring room, the operator pays particular attention to variation of the brightness information for a plurality of tuyeres in the circumferential direction of the blast furnace (deviation of the brightness in the blast furnace circumferential direction) so as to intuitively detect generation of abnormality in the vicinity of the respective tuyeres.
Patent Document 2 discloses a technique of adjusting a ratio between non-melted iron ore and coke that are put into a furnace from a furnace top based on a drop frequency detected by attaching cameras and brightness meters at equal to or more than three places among a plurality of tuyeres in the blast furnace circumferential direction and computing the number of times of drop of the non-melted iron ore from the upper side at the respective places.
Furthermore, Patent Document 3 discloses a method of providing combustion performance of pulverized coal by performing image processing on temperature distribution in a tuyere image shot by a radiation temperature camera as a technique replacing the sensory inspection by an operator. In the technique disclosed in Patent Document 3, the temperature distribution in the tuyere obtained by the radiation temperature camera is divided into a plurality of regions and a temperature-based area ratio, a black portion (pulverized coal uncombusted band) area ratio, and the like are digitized for each region so as to index the combustion performance of the pulverized coal.